Such a device for measuring current can also be designated as a current sensor, in particular then if it can be sold in the trade as a product consisting of one single component. Such a one-piece current sensor is known from U.S. Pat. No. 5,942,895. The current sensor consists of a current conductor, a magnetic field sensor for measuring the magnetic field produced by a current flowing through the current conductor and a ferromagnetic yoke. The magnetic field sensor contains a semiconductor chip with two magnetic field concentrators arranged on the surface of the semiconductor chip that are separated by an air gap and two Hall elements integrated in the semiconductor chip that are arranged on both sides of the air gap so that magnetic field lines pass therethrough that issue from the first magnetic field concentrator in the vicinity of the air gap and impinge on the second magnetic field concentrator in the vicinity of the air gap. The semiconductor chip contains in addition the electronic circuits necessary for the operation of the Hall elements and the amplification and processing of the voltage signals delivered by the Hall elements. The magnetic field sensor is arranged on the current conductor so that the magnetic field lines created by the current run approximately parallel to the surface of the semiconductor chip and therefore also parallel to the magnetic field concentrators. The yoke borders the current conductor on three sides and forms together with the two magnetic field concentrators a nearly closed magnetic circuit. The yoke and the two magnetic field concentrators form a magnetic amplifier that amplifies the magnetic field produced by the current. Disadvantages of this current sensor are that because of its construction as current sensor with integrated current conductor it is only suited for measuring relatively small currents of up to 20 A and that external magnetic fields are hardly screened.
From CH 659 138 a device for measuring the current flowing in a current conductor is known with which a screen of magnetic material with high permeability screens magnetic stray fields.